MicroRNAs (miRNAs) are a novel class of abundant small RNA elements with regulatory roles in gene expression. Estimates are that miRNAs constitute 1-4% of genes in animal genomes and that they may regulate as many as a third of all human genes. In addition, a recent study found that 70-90% of the genome is transcribed into RNA and that a significant percentage of these RNAs represent ncRNAs, including many unidentified miRNAs. However the roles of most miRNAs are unknown. Our recent work demonstrates that a C. elegans miRNA plays a significant role in longevity. Genetic studies in C. elegans have identified myriad genes and pathways that affect longevity. However, the extent of miRNA involvement in aging, and the genetic circuitry and mechanisms by which these genes modulate aging, has not been elucidated. This proposal will test the hypotheses that miRNAs play a fundamental role in life span by acting in aging pathways, and that their expression patterns provide novel biomarkers of aging. The proposed research targets an important biomedical area of research - aging - in the context of a fertile new field of biological research - miRNAs. Given the high conservation of miRNAs across species, it is likely that insights uncovered by this research will have high relevance towards our understanding of aging in higher organisms and may suggest new diagnostic and therapeutic avenues to treat diseases of aging in humans. In Specific Aim 1, we will test the hypothesis that additional known miRNAs function in regulation of C. elegans life span. Here we have examined the expression patterns of all C. elegans miRNAs and have uncovered significant expression changes of multiple miRNAs during aging. To study the role of these miRNAs in aging, we will characterize the life spans of mutants with loss or over-expression of our top aging-associated miRNA candidates. In order to understand the pathways affected by age-related miRNAs, we will search for targets of these miRNAs. In Specific Aim 2, we will test the hypothesis that novel miRNAs are expressed during aging and function in life span regulation? Although thousands of miRNAs have been identified in higher eukaryotes, it is likely that many more remain unidentified. In our cloning screen of aged C. elegans (Aim 1) we obtained nearly 500,000 small RNA reads that do not match known miRNAs. Preliminary bioinformatic analysis suggests many of these sequences may be novel miRNAs. In Specific Aim 3, we will test the hypothesis that miRNA expression patterns provide predictive value in determining future life span. Here, we propose to make GFP fusions to the promoters of miRNAs altered in aging and identify a few miRNAs whose expression at a particular time or in a particular tissue predicts future life span.